A conventional technology disclosed, for instance, by Japanese laid-open patent No. 2002-22671 optimizes the internal combustion engine's valve timing and valve lift amount in order to prevent the oil consumption amount from increasing (oil rising) at the time of internal combustion engine deceleration and inhibit the catalyst from deteriorating at the time of internal combustion engine deceleration.
When the throttle is closed, that is, when the driver makes a request for deceleration, the fuel is generally cut off in the internal combustion engine to improve the fuel consumption characteristic. Therefore, when the internal combustion engine decelerates, a considerable negative pressure is produced in the intake pipe, and air containing no fuel is distributed from the intake path to the exhaust path.
When a considerable negative pressure is produced within the intake pipe, it is likely that the in-cylinder pressure in the internal combustion engine will be rendered negative. If the in-cylinder pressure is rendered negative, the so-called oil rising occurs to increase the amount of oil consumption in the internal combustion engine. From the viewpoint of oil consumption amount minimization, therefore, it is preferred that the intake pipe pressure prevailing at the time of internal combustion engine deceleration be not rendered unduly negative. To this end, therefore, the intake air amount is increased with an increase in the engine speed at the time of deceleration.
Meanwhile, the catalyst positioned in the exhaust path of the internal combustion engine is likely to deteriorate when being supplied with a lean gas in a high-temperature environment. Therefore, it is preferred that the air distribution amount be reduced during internal combustion engine deceleration in order to inhibit catalyst deterioration during a fuel cut period.
The conventional system described above optimizes the valve timing and valve lift amount to reduce the air distribution amount at the time of internal combustion engine deceleration without making the intake pipe pressure unduly negative. The system, therefore, excels in minimizing the oil consumption amount increase due to deceleration fuel cut and inhibiting catalyst deterioration.
The applicant of the present invention is aware that the following patent documents including the above-mentioned patent document relate to the present invention:
[Patent Document 1]
Japanese laid-open patent No. 2002-227671
[Patent Document 2]
Japanese laid-open patent No. 1998-299518
[Patent Document 3]
Japanese laid-open patent No. 1998-115234
[Patent Document 4]
Japanese laid-open patent No. 2004-52677
However, the conventional system described above merely adjusts the valve characteristic, that is, merely adjusts the characteristic of a single actuator, to prevent the intake pressure from becoming unduly negative and reduce the air distribution amount although preventing the intake pressure from becoming unduly negative is contradictory to reducing the air distribution amount. In this respect, the above conventional system still needs improvement in oil consumption amount minimization and catalyst deterioration prevention.